The animal barns at the Canadian Agriculture Museum are free from November 1st to February 28th
The Canada Science and Technology Museum offers free admission on International Museum Day ( Monday May 18th this year) and on Canada Day (July 1st) in addition to free admission for children under the age of 4.
There are many wading pools across the city that are supervised and host daily activities and special events which includes a Water Play Program aimed at introducing swimming skills and water safety to children. They are free to use and a fun way to cool off in the summer. There’s one right by my work! They are not open all day long so check the site for locations and hours.